Reach, who has committed to play at the University of Georgia, shot 10-under par 62. His round featured one eagle and eight birdies. Reach, 18, is from Moscow, Pa., but attends a golf academy in Florida.
PGA Tour player established the Sage Valley record of 62 in November. Previously, former Augusta State star Vaughn Taylor held the record with 63.
Patrick Rodgers (67) and Nathan Kimsey (68) are the closest pursuers.
The 54-hole tournament boasts the top junior players from around the world and will conclude Friday.